Refining Trace Metal Temperature Proxies
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Earth and Planetary Science Letters 545 (2020) 116412 Contents lists available at ScienceDirect Earth and Planetary Science Letters www.elsevier.com/locate/epsl Refining trace metal temperature proxies in cold-water scleractinian and stylasterid corals ∗ Joseph A. Stewart a,b,c, , Laura F. Robinson a, Russell D. Day c,d, Ivo Strawson a, Andrea Burke b, James W.B. Rae b, Peter T. Spooner a,f, Ana Samperiz a,e, Peter J. Etnoyer g, Branwen Williams h, Adina Paytan i, Melanie J. Leng j,k, Vreni Häussermann l, Leslie N. Wickes g, Rachael Bratt a, Helena Pryer a a School of Earth Sci. Univ. of Bristol, Queens Road, Bristol, BS8 1RJ, UK b School of Earth & Environmental Sci., Univ. of St Andrews, KY16 9AL, UK c National Institute of Standards and Technology, Chemical Science Division, Hollings Marine Laboratory, Charleston, SC, USA d Marine Science and Nautical Training Academy (MANTA), 520 Folly Rd., Charleston, SC 29412, USA e Cardiff University, School of Earth & Ocean Sciences, Cardiff, CF10 3AT, UK f Department of Earth Science, University College London, London, UK g NOAA National Centers for Coastal Ocean Science, Charleston SC 29412, USA h Keck Science Department, Claremont McKenna-Pitzer-Scripps Colleges, Claremont, CA 91711, USA i Institute of Marine Sci., University of California, Santa Cruz, Santa Cruz, CA 95064, USA j British Geological Survey, Keyworth, Nottingham, NG12 5GG, UK k School of Biosciences, University of Nottingham, Loughborough LE12 5RD, UK l Huinay Scientific Field Station, Pontificia Universidad Católica de Valparaíso, Escuela de Ciencias del Mar, Facultad de Recursos Naturales, Chile a r t i c l e i n f o a b s t r a c t 18 Article history: The Li/Mg, Sr/Ca and oxygen isotopic (δ O) compositions of many marine biogenic carbonates are Received 7 February 2020 sensitive to seawater temperature. Corals, as cosmopolitan marine taxa with carbonate skeletons that Received in revised form 7 June 2020 can be precisely dated, represent ideal hosts for these geochemical proxies. However, efforts to calibrate Accepted 8 June 2020 ◦ and refine temperature proxies in cold-water corals (<20 C) remain limited. Here we present skeletal Available online xxxx 18 13 Li/Mg, Sr/Ca, δ O and carbon isotope (δ C) data from live-collected specimens of aragonitic scleractinian Editor: L. Derry corals (Balanophyllia, Caryophyllia, Desmophyllum, Enallopsammia, Flabellum, Lophelia, and Vaughanella), both Keywords: aragonitic and high-Mg calcitic stylasterid genera (Stylaster and Errina), and shallow-water high-Mg Scleractinia calcite crustose coralline algae (Lithophyllum, Hydrolithon, and Neogoniolithon). We interpret these data in Stylasteridae conjunction with results from previously explored taxa including aragonitic zooxanthellate scleractinia seawater temperature and foraminifera, and high-Mg calcite octocorals. We show that Li/Mg ratios covary most strongly Li/Mg with seawater temperature, both for aragonitic and high-Mg calcitic taxa, making for reliable and mineralogy universal seawater temperature proxies. Combining all of our biogenic aragonitic Li/Mg data with previous calibration efforts we report a refined relationship to temperature: Li/MgAll Aragonite = 5.42 exp(−0.050 × ◦ 2 ◦ T ( C)) (R = 0.97). This calibration now permits paleo-temperature reconstruction to better than ±3.4 C ◦ (95% prediction intervals) across biogenic aragonites, regardless of taxon, from 0 to 30 C. For taxa in this study, aragonitic stylasterid Li/Mg offers the most robust temperature proxy (Li/MgStylasterid (Arag) ◦ 2 ◦ = 5.64 exp(−0.046 × T ( C)) (R = 0.95)) with a reproducibility of ±2.3 C. For the first time, we show that high-Mg calcites have a similar exponential relationship with temperature, but with a lower ◦ intercept value (Li/Mg = 0.63 exp(−0.050 × T ( C) (R2 = 0.92)). This calibration opens the possibility of temperature reconstruction using high-Mg calcite corals and coralline algae. The commonality in the relationship between Li/Mg and temperature transcends phylogeny and suggests a similar abiogenic trace metal incorporation mechanism. © 2020 The Author(s). Published by Elsevier B.V. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/). 1. Introduction * Corresponding author at: School of Earth Sci. Univ. of Bristol, Queens Road, Bris- tol, BS8 1RJ, UK. Understanding the linkages between ocean circulation, car- E-mail address: [email protected] (J.A. Stewart). bon cycling, and rapid climate change on geologic and histori- https://doi.org/10.1016/j.epsl.2020.116412 0012-821X/© 2020 The Author(s). Published by Elsevier B.V. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/). 2 J.A. Stewart et al. / Earth and Planetary Science Letters 545 (2020) 116412 cal timescales remains a key goal of paleoceanographic research 1) however, Li/Ca and Mg/Ca are similarly impacted by calcifi- (Broecker, 1982). Paleo-seawater temperature is a hydrographic cation processes (Marchitto et al., 2018). Thus the ratio of coral variable vital to our interpretation of these ocean-climate inter- Li/Mg has great promise; preserving the temperature dependency actions (Thiagarajan et al., 2014). Much attention has therefore of these elements while minimising growth-rate effects (Case et been given to the development of geochemical paleo-temperature al., 2010). A universal Li/Mg relationship to temperature appears proxies in marine carbonates to extend temperature timeseries be- robust across published data for both zooxanthellate and azoox- yond the range of instrumental records (Anand et al., 2003; Case anthellate scleractinia (Andersson et al., 2020; Case et al., 2010; et al., 2010; Spooner et al., 2016). Deep-sea sediment cores remain Cuny-Guirriec et al., 2019; Fowell et al., 2016; Hathorne et al., a popular archive for obtaining ancient biogenic carbonate mate- 2013a; Montagna et al., 2014; Raddatz et al., 2013; Ross et al., rial (e.g. (Poggemann et al., 2017; Roberts et al., 2016)). However, 2019) and also aragonitic foraminifera (Hoeglundina elegans; Bryan impaired age control often limits use of these records for under- and Marchitto, 2008; Hall and Chan, 2004; Marchitto et al., 2018) standing the leads and lags of the climate system on millennial timescales or shorter. Therefore, robust temperature proxies from (Fig. 1A). This recalculated relationship is described by the equa- archives with precise age control are much needed. tion, Corals occupy a wide geographic and bathymetric range (Roberts ◦ = [± ] −0.049[±0.001]×T ( C) et al., 2006). They can be accurately and precisely dated by ra- Li/MgAll Arag (published) 5.27 0.06 e (1) diometric methods (Cheng et al., 2000) or annual growth band (R2 = 0.96;[±SE]) counting (Knutson et al., 1972) making them exciting targets for paleoceanographic research. Selected trace metal and stable iso- and is based on Li/Mg data compiled from the literature that topic ratios in marine carbonates have been shown to vary as we now adjust for interlaboratory analytical offsets (see Meth- a function of seawater temperature including: Sr/Ca (Beck et al., ods and Supplementary Information). More than three quarters of 1992; Cohen et al., 2001), Li/Ca (Hall and Chan, 2004; Marriott et the data characterising this Li/Mg relationship to seawater tem- 18 al., 2004), Mg/Ca (Anand et al., 2003; Case et al., 2010), and δ O perature however come from shallow-water coral specimens har- (Cobb et al., 2003; Gagan et al., 2012). Such temperature proxies bouring zooxanthellae (Fowell et al., 2016; Hathorne et al., 2013a; have been used to reconstruct temperature on sub-annual to mil- Montagna et al., 2014; Ross et al., 2019), with few observations lennial timescales (Cohen et al., 2001; McCulloch et al., 1999). obtained from azooxanthellate deep-water taxa (Case et al., 2010; Scleractinian corals (Subclass Hexacorallia: Order Scleractinia) Cuny-Guirriec et al., 2019; Montagna et al., 2014; Raddatz et al., calcify from an extracellular calcifying fluid (ECF) that is semi- 2013). Fewer still of these samples are from locations with well- restricted from ambient seawater (Sinclair and Risk, 2006). The characterised temperature (Case et al., 2010). Full characterisation chemistry of this ECF is modified via the Ca-ATPase pump, rais- of this relationship across multiple cosmopolitan cold-water coral ◦ ing internal pH and saturation state to promote precipitation of taxa (<20 C) from localities with well-documented hydrography skeletal calcium carbonate (Al-Horani et al., 2003). Such changes is therefore much needed. Cold-water corals are known to possess to internal seawater can impact skeletal chemistry independent of large heterogeneities in microstructural chemistry, with centres of 13 18 seawater temperature. For instance, the δ C and δ O composition calcification (COCs) being particularly enriched in Li and Mg and 13 18 of the coral skeleton is impacted by kinetic isotope effects during depleted δ C and δ O (Adkins et al., 2003; Anagnostou et al., hydration and hydroxylation of CO2 (Guo, 2020; McConnaughey, 2011; Chen et al., 2018; Correa et al., 2010; Gagnon et al., 2007; 1989), pH dependent dissolved inorganic carbon speciation (i.e. Stewart et al., 2016). It is important therefore to ensure that sam- − 18 2− HCO3 to O-depleted CO3 ; Adkins et al., 2003), and carbonic pling of such corals is reproducible and not unduly biased by mi- anhydrase activity (Chen et al., 2018). Skeletal trace metal compo- crostructures. sitions can be similarly modified by the balance between carbon- A second important, but poorly studied, deep-water coral fam- ate precipitation, direct seawater leakage, and ion pumping into ily is the Stylasteridae (Class Hydrozoa: Order Anthoathecata; the ECF. Through Rayleigh fractionation and/or growth entrapment, Fig. 2). These Hydrozoan corals differ significantly from scler- ions can become either depleted or enriched in the ECF (relative actinian corals in their ability to precipitate calcium carbonate to Ca) depending on their partition coefficient (D) into the car- skeletons of either aragonite, high-Mg calcite, or in some cases, = bonate lattice as calcification progresses (e.g.